You can use alternative firmware to increase the transmission power of your router and ensure a long range.
Ps : If you download an inappropriate firmware version or make a mistake during the installation, the router may quickly and irreparably be damaged.
Go to the website:
www.dd-wrt.com and click on the router database and look for your model and download the firmware file with extension ".bin". Before installation the new firmware detach all lan cables from the router except for the lan cable of the pc that has the firmware file that you have just downloaded.
Do a hard reset, now flash the firmware by typing 192.168.1.1 or certain routers have different default ip address, go to the firmware section and upgrade the firmware.
Lastly before you start the dd-wrt configuration, you will need to hard reset the router again.
Once restarted, you will see the firmware page..increase the specified value in the "TX power" field under the wireless/advance settings from around 71mW to a higher value in small steps. Upto 100mW is allowed by default, even though u can boost it to more than 200mW with further tweaking, but be careful; increasing this value will force your router's components to run at higher powers thus producing more heat.
As you have upgraded the router firmware, you have opended up a treasure chest of settings with new features etc.
Hope this helps. I read this guide @ chip this month issue..